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Surgery for Superior Canal Dehiscence Syndrome

Superior canal dehiscence syndrome (SCD) results from an opening (dehiscence) in the bone overlying the superior (uppermost) semicircular canal within the inner ear. With this dehiscence, the fluid in the membranous superior canal (which is located within the tubular cavity of the bony canal) can be displaced by sound and pressure stimuli.

There are normally only two points of increased compliance (yielding to pressure) in the inner ear: the oval window, through which sound energy is transmitted into the inner ear via the stapes bone; and the round window, through which sound energy is dissipated from the inner ear after traveling around the cochlea. SCD creates a third mobile window into the inner ear. Signs and symptoms of SCD result from the physiological consequences of this third window.

Vestibular and/or auditory signs and symptoms can occur in SCD. Vertigo and oscillopsia (the apparent motion of objects that are known to be stationary) evoked by loud noises and/or by maneuvers that change middle-ear or intracranial pressure (such as coughing, sneezing, or straining). Persons with SCD may experience a feeling of constant disequilibrium and imbalance, and may perceive that objects are moving in time with their pulse (pulsatile oscillopsia). Auditory manifestations of SCD may include autophony (increased resonance of one’s own voice), hypersensitivity to bone-conducted sounds, and an apparent conductive hearing loss revealed on audiometry.

The diagnosis of SCD is made based upon characteristic symptoms, specific findings on clinical examination, CT imaging, and findings on vestibular evoked myogenic potentials (VEMP) testing. The diagnosis should never be made exclusively on the basis of CT findings.

For many patients, avoidance of provocative stimuli such as loud noises may be sufficient treatment. For those patients who are debilitated by their symptoms, surgical plugging of the superior canal can be very beneficial in alleviating or substantially reducing the symptoms and signs.